1. Field of the Invention
The present invention relates to a high strength sintered silicon carbide molding.
More particularly, the present invention relates to a high strength sintered silicon carbide molding containing a rare earth element oxide and at least one member selected from the group consisting of oxides of aluminum, boron, beryllium, magnesium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, strontium, zirconium, niobium, molybdenum, technetium, barium, tantalum, tungsten and thorium in addition to starting materials used in the sintered silicon carbide molding disclosed in the inventors' prior Japanese Patent Application No. 44109/1981 (Laid-Open No. 160970/1982).
2. Description of the Prior Art
Because of its excellent high-temperature strength, thermal shock resistance, oxidation resistance, abrasion resistance and creep resistance, silicon carbide has been used for the production of heat-resistant moldings and heating elements for attaining a high temperature. Recently, the use of silicon carbide in the fields of high-temperature structural materials and abrasion-resistant materials has been increased remarkably.
However, it is difficult to obtain a sintered molding having a high denseness and strength from silicon carbide (hereinafter referred to as "SiC") per se, since SiC is difficultly sinterable. Therefore, in the production of such a sintered molding, there has been employed a process wherein Al.sub.2 O.sub.3, iron oxide, AlN, BeO, Be, B, B.sub.4 C, BN, Al or AlPO.sub.4 is incorporated as a sintering aid in the molding material and the mixture is hot-pressed or a reactive sintering process wherein a molding obtained from a powdery mixture of SiC with carbon is reacted with molten or gaseous silicon. However, the production of moldings having complicated shapes is difficult according to these processes and these processes are unsuitable for mass production. In addition, a non-compression sintering process has been proposed and employed recently as the most excellent process for the production of sintered SiC moldings. This process comprises adding carbon and boron as sintering aids to SiC powder, molding the mixture and sintering the resulting moldings without applying pressure as disclosed in, for example, the specification of U.S. Pat. No. 3,993,602.
In this process, boron carbide formed by the reaction of boron with carbon accelerates sintering of silicon carbide powder in the silicon carbide moldings. It has been known that even if an oxide used as the sintering aid in a hot press process is used in the non-compression sintering process, the sintering-accelerating, effect cannot be obtained at all. Generally, it has been considered that oxides are rather harmful to the non-compression sintering of silicon carbide.
The inventors previously found that rare earth element oxides, aluminum oxide and boron oxide are effective as sintering aids for silicon carbide. An invention attained on the basis of this finding was applied for patent as described above (Japanese Patent Laid-Open No. 160970/1982).